docs: def expect_constructor(target):
      """
      Set an expectation on a ``ClassDouble`` constructor
  
      :param ClassDouble target:  The ClassDouble to set the expectation on.
      :return: an ``Expectation`` for the __new__ method.
      :raise: ``ConstructorDoubleError`` if target is not a ClassDouble.
      """
      if not isinstance(target, ClassDouble):
          raise ConstructorDoubleError(
              'Cannot allow_constructor of {} since it is not a ClassDouble.'.format(target),
          )
  
      return expect(target)._doubles__new__